1. Field of the Invention
This invention relates to a strip product processing installation, and in particular an installation for acid pickling a metal strip.
2. Background Information
In the production of metal strips by rolling, it is customary at the end of rolling to pass the strip into a pickling line made up of a series of vats filled with a pickling liquid such as an acid solution.
The different elongated vats are arranged one after another along longitudinal feed axis of the strip, each vat being separated from adjacent vats by two bulkheads, respectively upstream and downstream, located at right angles to the strip feed direction, and each having, at its upper portion, a sill above the liquid to support the strip. The strip therefore follows an undulating path forming a loop in each vat which starting from the upstream sill, dips into the liquid and then emerges from the liquid at the other end to pass onto the downstream sill and dip into the following vat.
To maintain pickling efficiency, the acid solution, which progressively becomes charged with iron, has to be regenerated. Since the solutions contained in the different vats are titrated differently, the acid is generally made to circulate in counterflow fashion, the most downstream vat being fed with new acid and the most upstream vat returning the solution with the highest iron content to a regeneration installation.
Any risk of the strip becoming scored at each sill must also be avoided. To achieve this, the sills can be made up of deflection rollers turning about a horizontal axis perpendicular to the strip feed direction. Such rollers, however, must be supported by bearings that can become rapidly damaged on contact with the acid. For this reason fixed sills are generally used, the metal strip sliding on them as it passes from the upstream vat to the downstream vat, such a sill being made from a material that resists both the action of the acid and the wear caused by the passage of the strip.
However, the sliding of the strip on each sill can cause grooves detrimental to the surface state of the strip which must be kept as perfect as possible. This risk is averted thanks to the dynamic carrying forward, with the strip, of a certain quantity of liquid that forms a film that interposes between the strip and the sill. The strip is thus supported, on each sill, by a sort of liquid cushion and, in addition, the friction that might lead to wear and tear on the sill is reduced.
However, a certain amount of acid is also carried forward by the strip and passes from one vat to the next in the strip feed direction. This modifies the dosing of the solution in each vat, and may adversely affect pickling efficiency.
To overcome this drawback, each sill between two vats can be associated with drying rollers which limit the amount of acid carried downstream, but such a solution is relatively expensive and results in high maintenance costs, with the different moving parts working in an acid atmosphere. Such drying rollers can also cause the band to deviate. Moreover, while such an arrangement can be envisaged in new installations, it cannot easily be adapted to existing vats.
The invention provides a solution for all these problems thanks to simple arrangements which make it possible to perfect the working of the sills between the vats by preventing an excessive amount of acid being carried downstream and which, moreover, can be adapted to existing installations.